In recent years, apparatuses for detecting weak light are widely introduced to mainly medical scenes and research and development scenes. In such apparatus, a relatively expensive photomultiplier is often used as a detection unit of weak light.
Instead of the photomultiplier, an apparatus for detecting weak light by using a CMOS (Complementary Metal Oxide Semiconductor) image sensor that can be produced at a low cost has also been suggested (for example, see Patent Document 1).